The invention relates to a hot chamber die-casting machine for processing magnesium melts, with a casting container, a riser tube having a conical mouthpiece and a nozzle mounted on the mouthpiece, and a heating device for heating the nozzle and the mouthpiece area of the casting container.
In the hot chamber die-casting process, the casting container and the casting piston of the casting unit are located in liquid metal. As a result, the economy of the hot chamber process is much higher than in the cold chamber process.
It is also known that the material, magnesium, is easy to cast and is attractive for many applications because of its low weight. The processing temperature of magnesium, however, is between 630.degree. C. and 660.degree. C., depending on the alloy. Owing to this high temperature, it is necessary in hot chamber die-casting machines of the type mentioned above to provide heating, for the nozzle and the casting container. It is known that gas heat can be used to heat the nozzle and the casting container extension. This has certain disadvantages, however. Firstly, an open gas flame is present which must be monitored for safety reasons. It is also difficult to heat the nozzle with a constant temperature. This can result in deformation, especially bending of the nozzle. Heating with a gas flame can also result in decarburization of the very expensive material of which the nozzle and casting container are made. Therefore, a temperature control is required for the nozzle and casting container in order not to unnecessarily shorten the lifetime of the parts subject to wear. Open flames are especially undesirable when processing magnesium, for safety reasons.
Although heating systems have already been proposed that provide inductive high-frequency heating in the vicinity of the nozzle, in these proposals the extension of the casting container for the nozzle system is heated with gas. The above-mentioned disadvantages are then associated with gas heating employed in this manner. Since the inductors must be cooled with water in high-frequency heating, there is also a risk that water and magnesium will react with one another in an undesirable manner.
The goal of the present invention is therefore to propose a heating system for processing magnesium melts in a hot chamber die-casting machine that allows simple temperature monitoring and permits the desired high temperatures to be reached without adversely affecting safety.
To achieve this goal, in a hot chamber die-casting machine of the type mentioned above, provision is made such that an inductively-operating heating device is associated with the mouthpiece area of the casting container and the nozzle. All heating devices are operated at medium frequency (a frequency at the lower limit of high frequency), and the inductors are air-cooled. Hence, the invention is based on the idea that even relatively low frequencies are sufficient to generate the necessary heat and that lower cooling power, provided -by air, can suffice. The danger that water and magnesium will react with one another is thus reliably ruled out. Inductive heating makes it possible, in a relatively simple fashion, to achieve and perform uniform heating of the nozzle and casting container extension under temperature control. The operating frequencies for the heating device are of an order of magnitude between 8 kHz and 15 kHz.
In a preferred embodiment of the invention, the inductors can consist of helically wound, externally insulated copper tubes that are energized with electrical current and traversed by air. This design permits relatively simple manufacture of induction heating. An air inlet valve can be provided at one end of the copper tube while an air outlet valve is provided at the other end, with the latter opening more or less under temperature control, so that controlled air cooling of the inductors can be effected in a relatively simple fashion.
In a further preferred embodiment of the invention, the copper tube can be wound to form sleeve bodies that can then be slid in multiples onto cylindrical parts of the device to be heated. Thus, in an improvement on this idea, a sleeve body is pushed onto a cylindrical extension of the casting container in the vicinity of the mouthpiece, onto the area of the cylindrical nozzle adjacent to this casting container area, and onto the nozzle in the vicinity of its mouthpiece.
In yet another preferred embodiment of the invention, the sleeve body pushed onto the casting container extension can project externally beyond this extension, and surround externally at least the connecting area of the nozzle. In order to be able to detect any leaks, in an improvement on the invention, a monitoring unit for blooming magnesium oxide can be provided within the sleeve body projecting from the casting container and between the latter and the nozzle. The monitoring unit advantageously is designed as a ring with a contact loop. Although continuous heating is then provided from the casting container up to the nozzle mouthpiece, the risk of leaks in the nozzle assembly not being noticed and magnesium escaping are largely eliminated.
However, to make the seal as good as possible, in an advantageous embodiment, the conical connecting area of the nozzle can be provided with an O-ring for sealing in the vicinity of the conical mouthpiece of the casting container, and a sealing cord tensioned between two flange rings can be provided to seal the casting container cover off from the part of the casting container that projects from the latter, i.e. below the cylindrical extension. These measures contribute to the safety of the inductively heated casting unit.
In order to prevent any magnesium that might possibly spray out from penetrating into the vicinity of the inductors during the casting process, provision can be made such that at least the inductor associated with the nozzle is provided at its end facing the casting container with an edge that overlaps the forward edge of the inductor that extends to the mouthpiece area. By this means, any magnesium possibly spraying backward during the die-casting process can be reliably prevented from penetrating into the area between or under the inductors. In a preferred embodiment of the present invention, the inductor associated with the nozzle can also have a conical external contour that deflects any magnesium spraying rearward, forcibly outward.
In a preferred embodiment of the invention, the inductor extending to the mouthpiece area can be provided with an edge that overlaps the forward end of the inductor that rests on the cylindrical extension of the mouthpiece area. This edge can thus be formed in simple fashion by a flange provided with an annular surface extending diagonally in the direction of the forward end of the nozzle and up to the cylindrical area of the inductor. This annular surface also serves as a deflector for any spraying magnesium.
In another advantageous embodiment of the invention, an annular inductor can be provided in the vicinity of the crucible cover, said inductor being placed around the casting container to keep the temperature uniform and to make the method safer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.